1. Field of the Invention
The present invention relates generally to the field of printing press apparatus and more particularly to paper cutting and folding apparatus directly associated with continuous web printing presses.
2. Discussion of the Prior Art
Expensive, high speed printing presses are commonly used by commercial printing companies. Many such printing presses are fed from large rolls of paper and print on a continuous strip or web of paper, being thereby generally known in the industry as web presses. Full color web presses having several, serially arranged printing rollers for printing different colors and having output rates of about 40,000 printed articles per hour may, for example, cost between two and three million dollars each.
A web press typically requires use of an automated web cutting and folding machine which is connected to receive the printed web from the web press at web printing velocity. The cutting and folding machine automatically cuts the high speed web into sheets and folds the sheets one or more times into folded articles referred to in the printing industry as "signatures". These signatures may be sold as produced or may be delivered to other automated equipment which stitch or bind the signatures, often with other printed signatures, into booklets, magazines, books or the like. Because of their necessary complicated mechanical construction and electronic controls, such folders, known as signature folders, are very expensive and typically cost about 20 to 25 percent as much as their associated web presses.
Given the high cost of web presses and associated signature folders, it can be appreciated that the presses and folders must be capable of operating for extended periods of time at very high speeds in order to be cost effective and to produce finished signatures at industry competitive costs. Operation of the presses and folders at significantly below their maximum rated production speeds is, therefore, very inefficient from a cost standpoint.
Substantial problems which significantly limit folder and, hence, press speed are, however, commonly associated with high speed signature folder operation. These problems are principally associated with the second (quarter) fold and cause poor folding registration, thereby adversely affecting signature quality and causing additional problems in automated signature stitching and binding equipment in which many signatures are further processed before delivery to the customers.
To further explain the nature of problems encountered, it should be observed that many or most commonly used signature folders are constructed to perform two sequential paper folding operations. In a first folding stage the web, still traveling at printing velocity, is inserted along a fold line between first stage rollers which make the fold and cut the web. The cut and once-folded sheet is then usually folded again, in a second folding stage, perpendicularly to the first fold, the second fold being accomplished by a blade striking the already folded sheet along a second fold line and pushing the new fold between a pair of second stage rollers. Two stage folders constructed and operated in this manner are usually referred to as quarter folders since the resulting signatures are typically folded into quarters
Provision may also be made at in-feed regions of some types of quarter folders to longitudinally fold the web by passing it over a partial-width roller having an attached "plow". The resultant two layer, longitudinally folded web is then treated as a single layer web, being subsequently folded crosswise in the first folding stage and then folded again in the second folding stage. The resulting signature is thereby actually folded into eight, instead of only four sections. Although preliminary, longitudinal folding of the web may occasionally be done, for purposes of discussion herein such folding will be largely ignored as not materially affecting operation of the above-mentioned "first" and "second" folding stages.
The incidence of folding problems associated with the first folding stage is ordinarily no greater than might reasonably be expected for high speed folder operation. This is because when the first fold is made across a transverse fold line, the web of printed substrate is still intact and taut. There is, therefore, minimal opportunity for paper slippage, even if the web has been preliminarily folded lengthwise and the so-called "first" fold is, in fact, of a double thickness of paper.
As above mentioned, concurrently with making the first, transverse fold, the web is cut so that the second, perpendicular fold is of a free, folded sheet having at least two overlaying layers of paper. It can be readily visualized that when the two (or four) layered, folded sheet from the first stage is struck by the second fold blade and is thereby pushed between the second fold rollers, substantial opportunity exists for free ends of the overlayed layers of paper to slip sideways relative to one another. When such paper layer slippage occurs, the second fold for one or more paper layers will not be square to the first, transverse fold. As a result, when the signature is bound or cut into pages, the pages will be uneven and printing or drawings continuing from one page to the next facing page will be misaligned. Signatures misfolded beyond permissible, small tolerances must be manually sorted from the correctly folded signatures and discarded.
Moreover, to accommodate certain following operations on the signatures, the second fold may intentionally be made slightly off center so as to cause one side of the fold to be a little wider than the other side, the projecting side edge of the wider side being used for automated signature feeding and/or positional control. If second stage misfolds cause the intentionally projecting edge to be too narrow or wide, or to be non-parallel with the other edge, automated handling and feeding of the signature is impaired and equipment stoppage or jamming may occur.
Second stage folding problems in signature folders have typically been found to increase very rapidly as maximum printing speed of the associated web press is approached. Therefore, to maintain signature folder problems within acceptable limits, press speed must often be reduced to a level which does not produce competitively priced signatures.
In order to overcome such problems associated with signature folders, some large, high speed web presses have associated therewith two separate signature folders, each of which can, therefore, be operated at half the press speed. Although signature production rate can thereby be substantially increased over that obtainable by use of only one signature folder, equipment costs are very greatly increased. Furthermore, often quite valuable floor space is required for the second signature folder.
Recognizing both the importance of using only one signature folder for each of the most commonly used web presses, and the substantial second stage folding problems associated with presently available signature folders, press and folder manufacturers have attempted to reduce the above-discussed second stage folding problems by providing for scoring of the web along the second fold line before the first fold is made. For such pre-fold scoring, the web is passed through a paper scoring apparatus installed in the signature folder upstream of the first folding stage. The scoring apparatus typically includes a circular scoring blade mounted to one side of the web and a resilient roller mounted to the other side of the web. As the web advances between the rotating scoring blade and roller, a longitudinal indentation or groove is pressed by the blade into the web along a line concident with the subsequent second fold line. A fine jet of water may be directed onto the web along the intended score line to locally soften the paper and reduce the possibility of cutting or tearing thereof by the scoring blade.
The intent of this pre-fold scoring of the web along the intended second fold line is that the second fold will follow along the scored line and any tendency for one layer of paper to slip relative to the other (or others) will be thereby eliminated or greatly reduced. As a result, increased operating speed of the signature folders and web presses should be possible. In fact, such has not proven to be the case. Contrary to general expectations of web press users, it had been the general experience that not only does the above-described, longitudinal pre-fold scoring of the web not significantly reduce second stage folding problems but such scoring usually increases second stage folding problems.
In this respect, it can be demonstrated by quarter folding a sheet of paper that such uniform, pre-fold web scoring scores only part of the sheet in the correct direction for second stage folding. The other part of the sheet is actually scored in the wrong direction for the second fold. As a result, instead of being nested closely together, the two paper layers tend to be spaced apart at the second fold line by back-to-back scoring. The second fold blade then impacts the uppermost paper layer along a peaked score line instead of along a score line valley. As the blade pushes the two layers together to make the fold, the score peak line tends to be pushed sidewardly from under the blade, thereby causing even greater second fold misalignment than would be expected to occur without the pre-fold scoring. In some quarter folders, at the second folding stage the score lines of the paper layers may be peak-to-peak resulting in a similar, greater tendency for paper side slipping during second stage folding. Therefore, to Applicants' knowledge, signature folders utilizing the above-described, pre-fold web scoring must still be operated at web speeds well below the maximum rated web speeds of the associated web presses in order not to exceed acceptable signature reject levels.
For these and other reasons, Applicants have invented a greatly improved pre-fold web scoring apparatus for use in signature folders and which scores the web in alternating directions corresponding to the second fold direction for each layer of the paper.